Transmit power of a wireless transmit/receive unit (WTRU) may be determined in the WTRU based on measurements made by the WTRU and data received from an evolved NodeB (eNodeB). The WTRU transmit power control may be used for maintaining quality of service (QoS), controlling intercell interference, maximizing a WTRU's battery life and the like.
In Third Generation Partnership Project (3GPP) long term evolution (LTE), uplink (UL) power control may be used to compensate for long-term fading, (including path loss and shadowing), while reducing inter-cell interference, and avoiding occurrences of the WTRU having to invoke its maximum power procedure to prevent its power amplifier (PA) from operating beyond its linear region and/or to prevent the WTRU from exceeding maximum transmit power limits imposed by the network, regulatory requirements, and the like. LTE power control methods may include combined open loop and closed loop power control methods. In LTE Release 8 (R8) and 9 (R9), the WTRU transmits on a single carrier over one antenna which may be accomplished with one power amplifier (PA). Open and closed loop power control related data are exchanged between the eNodeB and the WTRU for the single transmit path.
In LTE R8 and R9, power headroom may be used for assisting the eNodeB to schedule the UL transmission resources of different WTRUs. In LTE, power headroom, reported from the WTRU to the eNodeB, is the difference between the nominal WTRU maximum transmit power and the estimated power for PUSCH transmission for the single carrier. Maximum transmit power imposed by the network for the single carrier is signaled by the eNodeB to the WTRU in system information. Additional limits such as the WTRU's power class, its PA capabilities, and the like, may reduce the maximum transmit power used by the WTRU for the headroom calculation.
LTE R8 and R9 methods for calculating and signaling power headroom and other power control related data may not be sufficient to support multiple component carriers (CCs) which may require multiple WTRU PAs.